[parser] Add missing handling of null-aware elements in if-else

Part of #55954

Change-Id: Ie22ff9ddf50f47e20b1cfbf11f01bdc900123619
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/388003
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Chloe Stefantsova <[email protected]>

pkg/_fe_analyzer_shared/lib/src/parser/literal_entry_info_impl.dart

@@ -254,6 +254,8 @@ class IfElse extends LiteralEntryInfo {
       return new Nested(ifCondition, const IfElseComplete());
     } else if (optional('...', next) || optional('...?', next)) {
       return const ElseSpread();
+    } else if (optional('?', next)) {
+      return new Nested(nullAwareEntry, const IfElseComplete());
     }
     return const ElseEntry();
   }

pkg/front_end/parser_testcases/null_aware_elements/nested.dart

@@ -0,0 +1,110 @@
+test1(List list, bool Function(dynamic) p, int? a) {
+  return {
+    for (var element in list)
+      if (p(element))
+        ?a
+  };
+}
+
+test2(List list, bool Function(dynamic) p, int? a, int? b) {
+  return {
+    for (var element in list)
+      if (p(element))
+        ?a
+      else
+        ?b
+  };
+}
+
+test3(List list, bool t, int? a) {
+  return {
+    if (t)
+      for (var element in list)
+        ?a
+  };
+}
+
+test4(List list, bool t, int? a, int? b) {
+  return {
+    if (t)
+      for (var element in list)
+        ?a
+    else
+      for (var element in list)
+        ?b
+  };
+}
+
+test5(List list, bool Function(dynamic) p, int? a) {
+  return {
+    for (var element in list)
+      if (p(element))
+        ?a: "value"
+  };
+}
+
+test6(List list, bool Function(dynamic) p, int? a, int? b) {
+  return {
+    for (var element in list)
+      if (p(element))
+        ?a: "value"
+      else
+        ?b: "value"
+  };
+}
+
+test7(List list, bool t, int? a) {
+  return {
+    if (t)
+      for (var element in list)
+        ?a: "value"
+  };
+}
+
+test8(List list, bool t, int? a, int? b) {
+  return {
+    if (t)
+      for (var element in list)
+        ?a: "value"
+    else
+      for (var element in list)
+        ?b: "value"
+  };
+}
+
+test9(List list, bool Function(dynamic) p, int? a) {
+  return {
+    for (var element in list)
+      if (p(element))
+        "key": ?a
+  };
+}
+
+test10(List list, bool Function(dynamic) p, int? a, int? b) {
+  return {
+    for (var element in list)
+      if (p(element))
+        "key": ?a
+      else
+        "key": ?b
+  };
+}
+
+test11(List list, bool t, int? a) {
+  return {
+    if (t)
+      for (var element in list)
+        "key": ?a
+  };
+}
+
+test12(List list, bool t, int? a, int? b) {
+  return {
+    if (t)
+      for (var element in list)
+        "key": ?a
+    else
+      for (var element in list)
+        "key": ?b
+  };
+}